Telegraph selector



Jan. l, 1946. ANGEL 2,391,868

TELEGRAPH SELECTOR Filed March 7, 1942 FIG. I

Hmmm I ATTORNEY Patented Jan. l, 1946 TELEGRAPH SELECTOR Herbert Angel, Brooklyn, N. Y., assignor to The Western Union Telegraph Company, New York, N. Y., a corporation of New York Application March 7, 1942, Serial No. 433,769

12 Claims.

This invention relates primarily to telegraph selectors, and more particularly to that type of selector that may be used on way-wire circuits having a plurality of way-stations associated therewith whereby any one of the stations may selectively communicate with any one or a number of the other stations on the way-wire.t

On a way-wire circuit such as along a railroad right of Way, the sending and receiving mechanisms which may be, for example, key and sounder sets, are, for obvious reasons, normally disconnected from the line. When a station Wishes to communicate with another, the sending and receiving mechanism thereat is connected to the way-circuit and a calling signa1 or signals transmitted which selectively operates selectors at the desired station or stations to operate visible and/or audible calling or signaling means thereat. On the operation of the visible and/or audible calling or signaling means at the called station or stations, the operator thereat connects his sending and receiving mechanism to the way-circuit and transmits an acknowledgment signal back to the calling station whereupon the calling station transmits the message. In this manner any station is permitted to selectively call any one or a number of the other stations without disturbing the uncalled stations. The selectors at each station on the way-wire respond to different predetermined signal .sequences so that each station may be selectively called. Selectors have been developed rwhich operate in the manner above described but are eX- tremely intricate in design, expensive to maintain because of the need of frequent servicing and adjustments, are relatively expensive to manufacture and require for their proper operation a signaling code wherein the individual signal impulses have a very deiinite timed relationship with each other.

1n accordance with the above, it is one of the primary objects of the present invention to provide a signal selector which is easy to manufacture and maintain, has few movingy parts and which may be easily changed to respond to a different calling signal.

Another object'of the invention is to provide a signal selector` which during the normal ow of traffic over the way-wire does not respond to the normal traic signals and is only operated following a predetermined line condition.

Another object ofthe invention is to provide a signal selector which responds to a relatively simple calling signal, as distinguished from the prior art devices which are operated in response to comparatively complicated calling signals.

Still another object of the invention is to provide a selecting device whereby more than one station may be selectively called in response to a single general calling signal.

These and other objects of the invention will be more apparent when taken in conjunction with the following detailed description and the accompanying drawing, in the latter of which:

Fig. l is a diagrammatic view of the essential elements of a selector constructed in accordance with the teachings of the present invention and the electrical circuits thereto; and

1 Fig. 2 is a diagrammatic view of a plurality of way stations on a way-wire circuit.

Referring rst to Figi, a way-Wire or circuit II is shown looped through a jack I2 and a line relay I3 as is the general arrangement at a Waystation. An answer set I4 has a cord I6 with a plug I1 associated therewith whereby on the insertion of the plug I1 in the jack I2 the answer set I4 may be connected in series to the wire in the well known manner. The answer set I4 may also include transmitting means and, if the way-wire is to be operated in response to Morse signals, the answer set I4 would include a key and sounder, or, if the Way-wire is t0 be operated in accordance with other types of signals, such as start-stop signals, the answer set I4 would include a keyboard and a printing mechanism.

The particular type of answering set employed in conjunction with the invention is immaterial, as will be apparent hereinafter, the only requirement being that means be provided therein or at other points to enable the origination of the calling signals in a manner pointedout. The tongue I8 of the line relay I3 is grounded, and the associated make stop is connected by a conductor I9 to one of the terminals of a magnet 2|. The other terminal of the magnet 2| is connected by a conductor 22 through a resistance 23 to a source of potential at 24. A condenser 2B of appropriate value is connected in parallel relation to the resistance 23. Also connected in parallel relation with the resistance 23 and condenser 26 by means of conductors 2T and 28 is a normally open contact 29. The contact 29 includes a stationary spring element 3| and a movable spring element 32. The spring element 32 tends to make contact with the spring element 3| but is normally held out of engagement therewith by an arm 33 of insulating material. The arm 33 is fixed to a collar 34 which in turn is attached by The shaft 36, which is suitably supported by means not shown, has adjacent its upper end, as shown in Fig. 1, a toothed ratchet wheel 33, which is fixed to the shaft for rotation therewith. In operative relation with the ratchet wheel 38 is a yoke member 33 with arms 4l and 42 dis posed onopposite .sides of the ratchet wheel 38.. The yoke member 39 is pivotally mounted on a pin 43 and has xed thereto an Varmature 44 in operative relation with the magnet 2 l. A spring 46 attached to the yoke 39 tends to pivot the same in a counterclockwise direction to hold the arm 42 in engagement with the ratchet wheel 38.

On energization of the magnet 2l in the manner hereinafter pointed out, it eiects pivoting of the yoke 33 a small amountin a clockwise direction to withdraw the arm 42 from engagement with the ratchet wheel 38 and move the arm 4l in engagement therewith. The design of the ratchet wheel 38 Aand the arms 4i and 42 i-s such that the engagement of the tip of the arm 4l with the ratchet wheel 38 causes the 'latter to advance or rotate a distance substantially equal to one-half the distance between two adjacent teeth. On the deenerg'ization. of the magnet 2|, the spring 46 rocks the yoke 39th withdraw the arm 4l from engagement with the ratchet wheel 36 and reeen gage the arm 42 therewith whereby the ratchet is stepped the remaining distance between two consecutive teeth. Thus, foreach energization and deenergization of the magst 2l, the ratchet wheel 3B and shaft 3.6 are stepped or rotated .an amount equal to the distance between two consecutive teeth Yon the ratchet wheel.

Secured'to lthe lower end of the shaft 36 by means of a set screw 45 is a colla-r 47 and extend'- ing from the collar `4l' is an arm 48 rotative therewith which is preferably made of insulating material. By means Vof the set screw 45 the relative position of the arm 48 on the shaft may he changed. In operative relation with the arm 48, is a normally open set .oi contacts 49 including spring elements I and 52.Y The spring element 5l is relatively stili, while the spring element 52 is more exible,and by means of the arm 48 it maybe moved into contact with the spring eleF Y nient 5I. Y The spring element 52 is connected to av ,source ,of positive potential at 53 while the spring. element `El is connected by means of a conductor 54 to the starter anode 56 of a, cold cathode type of vacuum tube 5l.A The tube 5l h'ajs a grounded lament 58 which is also conhected lby means of a conductor 5S through a condenser 6 l, in parallel relation with a resistance 62, to the conductor 54. The plate 63 of the tube '5? is connected through a normally closed key 64 'and the coil of a, signal relay 66 to positive potential at 6l. The tongue of the signal relay 66 is grounded and the make stop thereof is connected by means ci a conductor '68 through vsignaling or alarm means, such as fa bell 69 and/or signal lampV 7l, to a source of potential at '12.

The operation ofv the apparatus suchas that disclosed in Fig. 1 is as follows, assuming station A, Fig.- 2, at one end of the Way-wire H desires to call station C at some other point on the way# wire. Each of the stations A, B and C, shown in Fig. 2, has equipment such as that shown inv l, the 'only diierenfce -in the 'equipment' at the various 's'tations'"being the relative positions of :the arms v33 and 48 on the shaft 3B. which, in a manner hereinafter pointed out, permits calling or the successive calling in of a plurality of desired stations in response to a single general calling signal.

During normal operation of the way-wire circuit H for the transmission of regular intelligenee, the open and closed line conditions, and particularly the open line conditions, are of short duration. The line relay I3 responds to all line signals, hein-g energized on closed line .conditions and deenergized on open line conditions with its tongue i6 being operated in accordance with the energization and deenergization thereof. With the arms such as 33 of all the selecting mechanisms in their normal positions, such as that in of one station to the exclusion of the others, 75

,shown in Fig. l, the associated contact sets such as 29 are held open. While the contact sets 29 are open, the resistances 23 and condensers 26 at each stat-ion are in circuit with their associated mag-nets 2l. The resistances such as 23 and condensers such as 26 at each station are of such value that with the condensers 26 fully charged, as they will be when the tongues I8 of the Vline relays i3 engage associated make stops, the condensers 26 do not have time to .completely discharge through associated resistances 23 during the short open linek conditions .of normal signal intervals or while the tongue :I3 of .the line relay is away from its associated make stop.

When one station desires to call one or more other stations, the calling station opens the line il and keeps it open for at least a predetermined length cf time.. 'The opening of the line removes the grounded tongues i8 at -all the stations from contac-t with associated make stops, thus opening the circuits to all the magnets 2|.. This allows the charges on the c'ondensers 216 te be dissipated through associated resistances 2-3 and the values of the condensers and resistances 26 and ,23, .'respectively, at each of the vstations are such that the condenser-s are substantially completely discharged during the open line condition of at least the predetermined length. With the condensers 26 substantially Vcompletely discharged, the next closed line condition duringY which the circuits through the magnets 2| are completed permits a charging current to flow through thesaid circuit to charge the `condensers 26 which is of sucient value to operate the magnets 2;I. IThe normal short openings of the'line I-l during normal transmission are of insufficient length to permit sunricient discharge of the condensers 216 to require a charging current sufcient to operate the magnets 2|. Accordingly, the magnets 2| areonly operated on a closed line conditionfollowing an open line condition of at least a predeterminedlength.

The closed line condition following van open line vcondition of the predetermined vlength causes the energz'ation Vof the magnets such as 2.1 and the rocking of the yokes such as 39 which, .as hereinbefore described, efect rotation ofV the shafts '36 ,a half a tooth of the ratchet wheels A38, The next deenergi'zation o-f the magnet I2l in response to another open line'condition which may be of short Aduration eliects another half-tooth revolution of the shafts 36. This amount of -rotation of the shafts 36 permits the arms 33 rotating therewith to move out of operative relation with .associated contact'sets 23 whereby the .contacts are Vpermitted .to close. fThe closing of the contact sets29 .places a `direct shunt around the condensers 26 `and resistances 23, lwhich in effect removes them from the vcircuits to their 'associated magnets 2 l. With. the 'Contact A'sets' 2.9 close'dthe magnets 2l are responsive to all normal operations of the tongues I8 of the line relays I3, and hence the shafts 36 will be stepped one tooth for each subsequent opening and closing of the line I I. The shafts 36 rotate in synchronism with one another and at predetermined points in the revolutions thereof, a point being individual to each shaft, are effective in a manner hereinafter pointed out to operate a signaling and/or calling device at respective stations. Thus, the magnets 2I which are normally unresponsive to the normal intelligence transmitted over the way-wire I I are rendered operative by an open line condition of at least a predetermined length and thereafter are responsive to all further line openings, up to a certain number, which may be considerably shorter in duration than the length of the predetermined opening and of substantially the same length as those sent in transmitting normal intelligence. The manner in which the different shafts 36 at the various stations are effective to operate associated signaling equipment at different points in the rotation thereof will be pointed out in the following paragraphs.

The arms 48 on the shafts 36 at the various stations are each positioned differently with respect to the arms 33 so that the arms 48 close their associated contacts 49 after various degrees of rotation of the shafts 36. Let it be assumed that the arm 48 at station A, Fig. 2, requires the shaft 36 to step substantially three teeth before closing its contact set 49 and the arms 46 at stations B and C require rotation of the shaft 36 ve and eight teeth respectively before closing associated contact sets 49. With this arrangement, then station A in calling station C would effect rotation of the shafts 36 at all the stations on the way-circuit eight teeth and after the eighth step would hold the line open for an abnormal length of time so that the contact set 49 at Station C and only station C would remain closed for a corresponding interval. When a contact set 49 is closed at one of the stations such as at C, which is after the shaft 36 has rotated eight steps, the source of positive potential at 53 is effective to begin charging the normally uncharged condenser 6I. If the contacts 49 are maintained in the closed condition a sufficient length of time to substantially completely charge the condenser 6I, thereafter the starter anode 56 of the associated tube 51 becomes increasingly positive with respect to the grounded filament 58. When the potential difference is sucient between the starter anode 56 and the filament, the tube 51 becomes operative and this interval of time is dependent upon the capacity of the condenser 6I, the value of the resistance 62 and the charging rate from the source potential at 53. The tube 51 in the preferred embodiment of the invention is of the type that when once put in a conductive condition remains in this condition until the circuit to the plate or filament is interrupted, and when once made conductive is independent of the starter anode 56.

The operation or conductive conditioning of the tube 51 effects energization of the signal relay 66, which through its grounded tongue completes a circuit through the associated make stop and the signaling or alarm mechanisms such as the bell 69 and the signal lamp 1I to potential at 12. The operation of the alarm mechanisms calls to the attention of the attendant at the associated station that some other station desires to communicate therewith whereupon he inserts the plug I1 of his answer set into the associated line jack I2 and sends an acknowledgment signal. The operator at the answering station also operates the key 64 to open the circuit through the tube 51 whereupon the tube becomes non-conductive and the alarm circuit is restored to its normal open condition as the acknowledgment signal effects rotation of the shaft 36 from the position in which it closed the contact set 49.

In order to call station C which requires the shaft 36 to rotate eight teeth before the arm 46 closes the contact set 49, the Contact set has to remain closed for a sufficient length of time to allow the condenser 6I to become charged and the starter anode 56 sufciently positive with respect to the filament 58 to start the tube 51 into operation. Accordingly, a calling operator when calling a station such as C leaves the line open a sufficient length of time after the contact set 49 at station C has been closed to permit the associated condenser 6I to become charged. Thus in calling station C which requires its shaft 36 to rotate eight teeth, eight open line conditions are transmitted which are separated by closed line conditions with the eighth open condition of sufficient length to permit the charging of condenser 6I. The rst precalling long open line condition which is transmitted prior to the following calling signal removes the resistances 23 from the circuits of the magnets 2| in the manner hereinbefore described and the operating characteristics of the magnets 2| are such that the following operating impulses of the calling codes need not be of such prolonged length. The values of the resistances 23 and condensers 26 are such that the predetermined precalling open line condition may be in the neighborhood of eight to ten seconds while the open line and closed line conditions of the calling signal may be in the neighborhood of a small fraction of a second. rIhe last open line condition of a calling signal may be in the neighborhood of three or four seconds, depending upon the characteristics of the tubes 51 and the value of the condensers 6I and resistances 62.

When calling a station such as C which requires eight steps of the shaft 36 to close its contact set 49, other stations such as station B which may require only five steps of its shaft 36 to close its contact set 49 are not called because of the fact that the contact sets 49 at a station such as B are only closed momentarily by one of the short open line conditions in stepping the shafts 36. The brief closing of the contact set 49 at station B is not of sufcient length to permit the charging of the condenser 6I thereat so that the starter anode in tube 51 is not rendered sufficiently positive to make the tube operative. Thus station A may call in a station such as C to the exclusion of another station such as B having a calling code of a lesser number of signals.

At times it may be desirous for a station such as A to call in a plurality of other stations such as stations B and C substantially simultaneously, as station A may have intelligence which should be received at both stations B and C. In order to effect the calling in of two or more stations, the calling operator need not send a separate calling signal for each station called as the calling signal for one station may be employed as part of the calling signal for another station. If, for example, station A were calling stations B and C simultaneously, station A would leave the line II open for three or four seconds on the fifth opening after the first precalling open signal which would call in station B, and then send two more short openings followed by a prolonged opening to call station C. The tubes 51 at stations B and C would become operative on the fth and eighthopenings of the line circuit which were ofk longer length than the other calling signals. The tubes 51 at stations B and C becoming loperative would operate associated alarm devices and in this manner any number or all ofthe other stations on the way-wire may be called substantially simultaneously by any one of the stations. Thus the calling operator does not have to send a separate calling signal to call in each station when desiring to call in more than one ata time.

VAfter a station or anumber of stations have been called, the intelligence signals transmitted over the way-wire. Hwhich may be an acknowledgment, are eiective to operate the magnets 2| which in turn step the shafts 36. kThe normal intelligence impulses step the shafts 35 until the arms 33 thereof engage and open associated contacts 29. The opening of the contacts 29 removes the shunts around the resistances 23 whereupon further intelligence impulses, which' are of short duration, are ineffective on the magnet 2| and accordingly the shafts 3S remain in their normal positions. 'Ihe rotation of the shafts 36 to the normal positions also rotates the arms 48 whereupon the particular arm operating its associated contact t9 permits the same to open whereupon the charged condenser 6l is permitted to discharge through its associated resistance E2. Thus all the selectors are returned to their normal` positions and will not be started into operation until an open line ccndition of considerable length is transmitted. In the event an open line condition of suincient length to start the selectors intooperation in the manner hereinbefore set forth is accidentally transmitted, none of the stations onthe circuit would be called unless another open line condition o considerable length were transmitted shortly after the transmission of the rst long open line condition. Normal message impulses transmitted following the accidental long open line condition would step the shafts 36V and the arms 48 would only close their associated contacts49 for afshort-interval of time which would be less than that required to render their associatedV tubes 51 operative.

rlhus in accordance with` the invention a selector is provided which normally does not respond to signals transmitted over the line and'v such an arrangement has the advantage in that wear on the selectors is lessened and they are always at their normal positions ready to respond to a calling signal.. The above arrangement also has an advantage in that any leakage in the condensers 26 during the short openings of the circuit Il and the transmission of normal intelligence is notr effective on the magnets-2l as the normal openings are of short duration and the condensers are recharged on thesubsequent closing of the line. Instead of the above described arrangement wherein a calling signa1 is terminated by a long open line condition, a closed line condition could be employed by changing the position ofthe arms- 48 on the shafts et a slight amount-cr the distance of approximately one-half tooth of the ratchet wheels 38. Similarly, the calling signal to whichA al particular selector mechanism selectively responds may be changed by changing the relative positions of the arms 33 andvl on the shaft 36. l

Y -It is obvious that various modifications of the apparatus andv circuits shown ,and` describedl herein may be made without departing from the spirit or essential attributes of the invention, and it is desired, therefore, Vthat only such limitations be placed thereon as are imposed by the prior art or are specifically set forth in the appended claims.

What is claimed is: 1; In a telegraph system of the type described, a line circuit, means. for transmitting signals over said circuit, a line relay responsive to said signals, an electromagnet having the coil thereof connected to contacts controlled by saidline relay, a condenser in said electromagnet circuit, a. resistance permanently connected in shunt relation with said condenser, means including said condenser and resistance for rendering said electromagnet unresponsive to the operation of said line relay in response to line signals of less than a predetermined length, and means responsive to a line signal of at least said predetermined length for disabling said last mentioned means to render said electromagnet unresponsive to operations of said line relay whereby said electromagnet is responsive to all operations'v of said line relay up to a predetermined number.

2. In a telegraph system, a line circuit, a line relay responsive to signals transmitted overL said line, an electromagnet, a first control meansy for said electromagnet including contacts operated by said line relay, a second control means for said electromagnet including a condenser and a resistance permanently connected in shunt re. lation with said condenser, means includingboth `of said control means for operating said .electromagnet a first time only after theA existence of a predetermined condition of saidV rst control means for at least a predetermined length of time wherein said condenser assumes a substantially stable condition, and means controlled by the first operation of said electromagnet to place thecontrol thereof solely under said first control means.

3. Ina telegraph system, a line circuit, a line relay controlled by signals transmitted over said line circuit, an electromagnet, means including contacts controlled by said line relay for completing a circuit to said electromagnet, a condenser and a resistance-in shunt relationtherewith in said electromagnet circuit, said resistance being` of such aV valueV as to prevent sufcient current to normally flow in said circuit to operate said electromagnet, means including said resistance to substantially discharge said condenser on the opening of said electromagnet circuit for at least ar predetermined length of time, means including the charging of said condenser to permit the passage ofsuilcient current through said electromagnet circuit to operate said electromagnet on the closing of said Vcircuit by said line relayr contacts following the substantial discharge .of said condenser, normally open shunting contacts for said condenser and resistance, and means controlled by the operationofv sa-id electromagnet to control said shunting-contacts to shunt said condenser and resistance in said electromagnet circuit whereupon said electromagnet follows the operation of said line relay contacts.

4. A telegraph system, a line circuit, a line relaycontrolled by signals transmittedover said line circuit, an electromagnet, means including contacts controlled by said line relay for completing a circuit to said electromagnet, a condenser and.k a resistance in shunt relation therewith `in said electromagnetv circuit, an armature associated with said electromagnet, means including said reslstance to normally limit the flow of current in said electromagnet circuit to such a low value as to prevent the operation of said armature by said electromagnet on the closing of the circuit thereto by said line relay controlled contacts, means including said resistance to effect substantial discharge of said condenser on the opening of said line relay controlled contacts for at least a predetermined length of time, means including said condenser in a substantially discharged state to permit the passage of sufficient current through said electromagnet circuit for said electromagnet to operate said armature on the closing of said line relay controlled contacts following the opening of the same for at least said predetermined length of time, and means controlled by operation of said electromagnet armature to shunt said condenser and resistance whereby the armature of said electromagnet is operative thereby under the direct control of said line relay controlled contacts.

5. The combination as set forth in claim 4 and including a normally inoperative alarm device and other means controlled by the armature of said electromagnet for rendering said alarm device operative.

6. 'Ihe combination as set forth in claim 4 and including a normally inoperative alarm device and other means controlled by a predetermined nurnber of operations of said armature following the said first operation thereof for rendering said alarm device operative.

'7. In a telegraph system, a line circuit, a line relay controlled by signals transmitted over said line circuit, an electromagnet, means including contacts controlled by said line relay for completing a circuit to said electromagnet, a condenser and a resistance in shunt relation therewith in said electromagnet circuit, an armature associated with said electromagnet, means including said resistance to normally limit the flow of current in said electromagnet circuit to such a low value as to prevent the operation of said armature by said electromagnet on the closing of the circuit thereto by said line relay controlled contacts, means including said resistance to effect substantial discharge of said condenser on the opening of said line relay controlled contacts for at least a predetermined length of time, means including said condenser in a substantially discharged state to permit the passage of sufficient current through said electromagnet circuit for said electromagnet to operate said armature on the closing of said line relay controlled contacts following the opening of the same for at least said predetermined length of time, a rotatable member having a normal position and rotated a predetermined amount on each operation of the armature of said electromagnet, a set of normally open contacts in shunt relation with said condenser and resistance and means controlled by the rotation of said rotatable member in rotating from said normal position to effect closure of said condenser and resistance shunting contacts whereby after the closing thereof the armature of said electromagnet is operative under the direct control of said line relay controlled contacts.

8. In a .telegraph system, a line circuit, a line relay controlled by signals transmitted over said line circuit, an electromagnet, means including contacts controlled by said line relay for completing a circuit to said electromagnet, a condenser and a resistance in shunt relation therewith in said electromagnet, circuit, an armature associa'tedwith said electromagnet, means including said resistance to normally limit the ilow of current in said electromagnet circuit to such a low value as to prevent the operation of said armature by said electromagnet on the closing of the circuit thereto by said line relay controlled contacts, means including said resistance to eiiect substantial discharge of said condenser on the opening of said line relay controlled contacts for vat least a predetermined length of time, means including said condenser in a substantially discharged state to permit the passage of suflicient current through said electromagnet circuit for said electromagnet to operate said armature on the closing of said line relay controlled contacts following the opening of the same for at least said predetermined length of time, a rotatable member having a normal position and rotated a predetermined amount on each operation of the armature of said electromagnet, a set of normally open contacts in shunt relation with said con- -denser and resistance, means controlled by the rotation of said rotatable member in rotating from said normal position to effect closure of said condenser and resistance shunting contacts whereby on the closing thereof the armature of said electromagnet is operative under the direct control of said line relay controlled contacts, a second set of contacts controlled by said rotatable member, an alarm device controlled by said second set of contacts and means including said second set of contacts for rendering said alarm device operative following a predetermined amount of rotation of said rotatable member from normal position.

9. 'I'he combination as set forth in claim 8 and including means for varying the predetermined amount of rotation of said rotatable member from said normal position to operate said second set of contacts to render said alarm device operative.

10. The combination set forth in claim 8 and including a time delay device and means including said time delay device and said second set of contacts for rendering said alarm device operative only on the operation of said second set of contacts at least a predetermined length of time by said rotatable member, said prolonged operation of said second set of contacts being effected by the cessation of operation of the armature of said electromagnet for said last predetermined length of time.

11. In an impulse receiver for a remote control system, the sub-combination of a relay, electrical circuits adapted to operate said relay in response to signal impulses received by said receiver, a condenser associated with said circuits and normally arranged to be charged at each signal impulse and to delay operation of said relay while being charged, whereby said relay is normally unresponsive to an impulse of less than a predetermined duration, and switching means connected to said condenser and controlled by operation of said relay to disconnect said condenser from said circuits when said relay is once energized, whereby said relay then becomes responsive to impulses of shorter duration.

12. In a impulse receiver for a remote control system, the sub-combination of a relay, electrical circuits adapted to operate said relay in response to impulses of variable length effective to change the normal condition of said circuits for Variable periods of time, a condenser associated with said 4circuits in a manner to have its state of charge controlled variably by the variable time conditions of said circuits and to in turn effect by its variable state of charge the response of said circuits to the 6 @senses time duration of said. changes; and. thereby prevent the operation ofl said relayin response to short changes in the condition of. said circuits in response to short impulses and switching means operated by said relay aiter it responds to a. long change in condition of said circuits eiective to vsl-isassociate the condenser from said circuits in a. manner to render the state of charge on the condenser independent. of the changing conditions of the circuits and to render the state of condenser charge ineective upon the operation of the relay in response to following changes in the condition of the circuits.

HERBERT ANGEL. 

